Question

List some evaluation projects for which nonprobability sampling might be appropriate.

Answer 1

Non-probability sampling is a sampling technique where the samples are gathered in a process that does not give all the individuals in the population equal chances of being selected.

1. Purposive Sampling (or Purposeful) This is sampling with a purpose in mind. We usually would have one or more specific predefined groups we are seeking.

EXAMPLE:-

if you are evaluating the attitudes of drivers towards speeding, you may want to only sample those who have got penalty points. Or, you could sample those with extreme characteristics by only selecting drivers who have been disqualified as a result of multiple offences.

2. Snowball sampling-A type of purpose sampling where existing participants recruit future subjects from among their acquaintances

EXAMPLE-

if you wanted to interview a sample of vegetarians/cyclists/people with a particular disability/people that support a particular political party or the homeless, your initial contacts may well have knowledge of other. In these cases you are not likely to be able to find good lists of people of these characteristics within a specific geographical area. However, if you go to that area and identify one or two, you may find that they know very well who the others in their vicinity are and how you can find them. This makes it easier to contact people you might not otherwise have any way of getting in touch with. However, it does introduce a lot of bias into your results because your samples are all likely to know each other and to have similar opinions.

3. Quota, , you divide the population (e.g. older drivers) into distinct parts (strata). You then decide how many of each stratum you want to have in the total sample.

EXAMPLE:-

you could stand outside an out-of-town supermarket in the day time. You have decided that you want to survey 50 male drivers aged over 65. Every time you see a male older driver enter the store you ask if he is aged over 65 and you continue until you reach your quota of 50 completed surveys. This is the non-random form of stratified sampling.

ABOVE ARE THE EXAMPLES WHICH ARE APPROPRIATE FOR NON-PROBABILITY SAMPLING.